Magnetic tunnel junctions(MTJ) are fabricated as a function of the input power of Al thin film. Al thin films have pseudo-crystalline structure at 30, 60, 90 W and transform into amorphous like smooth nanocrystalline state at 120 W. Junction resistance increases as the annealing temperature increases up to 250 degreesC and decrease at 300 degreesC at the pseudo-crystalline barrier. When the barrier has amorphous like nanocrystalline structure, optimum annealing temperature increases up to 300 degreesC. The barrier characteristics are strongly related with the microstructure of AlOx barrier.